K1 Noise Blanker and Blown Final?

I finished the KNB1 noise blanker today and installed it in the K1. When finished, I connected the K1 to my ATX-1080 set to the 40 meter band. I put the OHR WM-2 wattmeter and the T1 antenna tuner in between the K1 and the antenna. First I tried to put the T1 into bypass mode, but I wasn’t quite sure whether the yellow LED meant bypass on or tuner on… Later I found out that green led means tuner on, yellow led means bypass on.

On the receiver side everything was all right. I could toggle between OFF/HI/LO in the NB menu of the K1. When I tried to set the K1 in tune mode, the power supply tripped because of too high current draw from the K1. The current limiter was set to around 1.5 amps I think. I increased the limit but after that the K1 display showed P0.1 every time I tried to tune. The receiver was still all right.

What happened??? Did I manage to blow my final with too high SWR? Could the SWR really be that high with the ATX tuned to 40? I tried to switch to a dummy load but still only P01 on the K1 display when in tune mode.

Oh, well, I sent an email to the elecraft reflector and now I am awaiting for a reply. In the mean time I will re-do the transmitter checks from the beginning, ie. RF board part 2.

Speaking of the KNB1, there are two things I would like to mention. First, according to the errata sheet, I have to mount C14 on the bottom of the board between pins 1 and 8 of U1. This has to be done before U1 is mounted. If so, how on earth would I be able to mount U1? Surely the holes for pin 1 and 8 will be filled with tin if I solder a capacitor befire I solder U1 in. So, I waited with mounting C14 till after U 1 was in place and I think that was a good decision. Second, the noise blanker board has to be secured using a screw and a standoff. The standoff is installed with a internal-tooth lock washer and a nut. It looks to me, however, that it is impossible to mount the nut and the lockwasher without them touching a close-by circuitry. I wonder whether the green paint is destroyed when tightening the nut…

Besides that, the noise blanker appears to work. I didn’t actually remove any noise yet, but I can at least tune the circuit by adjusting the variable capacitor. So something is happening in there.

Ok, now back to the work bench and do the transmitter checks.

Author: Alexandru Csete

Embedded software engineer in the satcom industry during the day. Radio amateur and SDR hacker during the night.